Are you a bouba or a kiki?

Look at the spiky shape and the blobby shape. Which one is called kiki? You probably knew right away, and that is the whole trick. Nobody taught you.

In 1929 the psychologist Wolfgang Köhler showed people a jagged shape and a curvy one and asked them to match made-up words to each. They agreed. In 2001 Vilayanur Ramachandran and Edward Hubbard used the words kiki and bouba, and about 95% of people picked the same way.

It travels. A study of 917 speakers of 25 languages found most people show the effect, whatever language or alphabet they grew up with. It starts early too. Children as young as two and a half seem to do it, and in 2026 researchers reported chicks less than a day old doing it as well.

Nobody is sure why. Say both words in a mirror: your lips go round for bouba and pull tight for kiki. Another idea is that round things bounce with a low, smooth sound and spiky things clatter. The same pattern shows up in taste, where sweet tends to feel round and sour feels angular, and in faces, where people expect a Bob to look rounder than a Kirk.